This application claims the priority of German patent document 199 33 317.3, filed Jul. 16, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and an apparatus for determining the acoustic spatial characteristics of an enclosure, particularly of a vehicle occupant compartment in a motor vehicle.
For example, in the case of audio and video receivers for hi-fi playback, methods are known which permit one-time manual or automatic adjustments to be made at the equipment which is playing back the useful sound, for a spatial adaptation. In one known manual adjustment technique, for example, the spatial measurements, the locations of the loudspeakers and/or the reflection condition of the walls can be input to the equipment. In a known automatic adjustment arrangement, a special test sound is emitted when the hi-fi equipment is installed, and the analysis sound then received by means of a microphone, is analyzed to determine the spatial sound parameters. The latter are then correspondingly stored by means of a spatial sound processor, for the playback of a space-adapted useful sound.
When using the known methods in motor vehicles, the problem arises that the spatial acoustics in the vehicle occupant compartment change constantly; for example, as a function of the number and movement of the vehicle occupants, noise-affecting environmental influences (e.g., wind noise), temperature fluctuations, road conditions, or operating parameters of the motor vehicle, (e.g., vehicle speed or rotational engine speed).
Furthermore, methods are known for the active sound compensation by means of digital adaptive filters which, however, usually adapt too slowly to compensate the disturbing noises which often change very rapidly in the vehicle.
It is an object of the invention to optimize the sound quality of acoustic systems in motor vehicles, such as CD and radio playback equipment or handsfree telephone systems, in a simple manner in the sense of a dynamic space adaptation.
This and other objects and advantages are achieved by the method and apparatus according to the invention for determining acoustic spatial characteristics (particularly in a vehicle occupant compartment in a motor vehicle), in which a piece of equipment which normally emits a useful sound (such as music) also emits a test sound, in a psycho-acoustic masking range of the useful sound. Subsequently, the total sound, consisting of the reflected useful sound and the reflected test sound, is recorded as analysis sound. Finally, the reflected test sound fraction of the analysis sound is analyzed (in a known manner) with respect to the acoustic spatial characteristics. Preferably, particularly post-masking in the time domain and/or simultaneous masking in the frequency domain are utilized. Although the utilization of the pre-masking is a possible alternative, it is too complicated.
The test sound can be emitted simultaneously with the useful sound (for example, during a piece of music), the test sound becoming inaudible as a result of the so-called masking effect of the useful sound.
For background information on the nature of the psychoacoustic masking, reference is made to the xe2x80x9cPsychoacousticsxe2x80x9d Textbook by E. Zwicker, Springer Publishers, 1982, particularly Pages 35, and on, and Pages 94, and on.
In one embodiment of the invention, the masking range of the useful sound is determined in a useful-sound analysis block. A test sound is then defined which is adapted for the determined masking range, before the useful sound and the test sound are emitted. For example, within a piece of music, as a function of individual sections of the piece of music (the useful sounds), for example, with particularly wide covering ranges, several test sounds are emitted several times.
By means of the invention, the spatial characteristics, and thus the spatial transmission characteristics, are dynamically adaptively determined and compensated. This takes place by means of arbitrarily frequent test sound emission during a useful sound playback which can take place by the selection of the respective test sound in the inaudible range.
Also, as a result of the invention, simultaneous compensation of dispersions of the electroacoustic components (such as the loudspeaker, the microphone, the transducer or the amplifier) is possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.